Which TT will take me to the next level

1.New-Marantz TT-15! Designed by Marantz and built for them by Clearaudio-$1600, contoured acrylic table with an outboard motor, sophisticated tonearm with an Ebony arm wand. TT-15 comes with an $800 Clearaudio Virtuoso Ebony Wood Cartridge. Very good value. Plus, you get a very nice cart. in asking price.
2.VPI - bottom shelve. $1000 used with a nice $500 cart.
3. Lenco - If you have the skills. I think with the right plinth and research it can be a killer. Working on one, right now.
4. Modify what you have right now.
Here is an example of a table that I almost got rid of.
Invested about a $1000 in arm and cart. Plinth is a butcher block that cost me $35 each. One used for plinth and the other for stand. If you have a weekend or two to spare - some tools and basic skills, that might be the way to go.

http://cgim.audiogon.com/i/vs/i/f/1194752302.jpg

Cheers
Mariusz.

You can try Rega RB-300, Linn Ittok (used) , Morch up-4 or Advanced Analog MG-1 Linear Arm Tonearm ($650 + $150 for Air pump). Cartidge - Denon DL103-R is great and inexpensive ($350), Audio-Technica OC-9 $450, Benz Micro MC20E2 ($200) also above recommendations of Dynavector 20X cartridge ($650).
I REALY THINK YOU SHOULD KEEP YOUR "TT".
With small adj. in vibration control, upgrade cart. & arm - this TT will be really nice. I would not worry about spending $$$ on new cart & arm. If you decide to get a new TT in the future, you can always use it with new TT.
Improve vib. control.
Easiest way - 4" Butcher block (doesn't matter what species) with cones, spikes or isol-pads (choose what sounds best in your set-up). Good quality mat (like Genesis168 suggested) also helps. Also, you can invest in Cartridge Man isolator ($150) for cartridges $500 & below.
As you can see, sky is the limit. Start small and move up in small steps. Experiment. Change few arms and cartridges, play with different iso. products. It will help you understand better how TT works and what works. That's what I did. However, I am far from expert but I am starting to slowly figuring out what is what and how. I have tree TT in my basement with parts all over the place. Just thinking how can I improve the already good design. LOVE IT.